The present invention relates to a device mounting substrate in which a defective device has been repaired with a repair device and a method of repairing the defective device, and to an image display unit using the device mounting substrate and a method of producing the image display unit.
The production of an image display unit by arraying light emitting devices in a matrix to build up the devices into the image display unit has been generally performed by two methods. One method, which is used for producing liquid crystal displays (LCDs) or plasma display panels (PDPs), is carried out by directly forming devices on a substrate. The other method, which is used for producing light emitting diode (LED) displays, is carried out by packaging each LED, and arraying the single LED packages on a substrate. For example, in the case of producing image display units such as LCDs or PDPs, since device isolation is impossible from the viewpoint of the structure thereof, respective devices are generally formed, from the beginning of the production process, in such a manner as to be spaced from each other with a pitch equivalent to a pixel pitch of a final image display unit.
On the other hand, in the case of producing LED displays, LED chips obtained by dicing are individually connected to external electrodes by wire-bonding or bump-connection using flip-chip, to be packaged. In this case, before or after packaging, the LED chips are arrayed with a pitch equivalent to a pixel pitch of a final image display unit; however, such a pixel pitch is independent of the pitch of devices at the time of formation of the devices.
Since LEDs (Light Emitting Diodes) as light emitting devices are expensive, an image display unit using LEDs can be produced at a low cost by producing a number of LEDs from one wafer. To be more specific, the cost of an image display unit can be reduced by preparing LED chips while reducing a size of each LED chip from a conventional size of about 300 μm square into a size of several ten μm square, and connecting the LED chips to each other, to produce the image display unit.
From this viewpoint, there have been known various techniques of transferring devices densely formed on a substrate to a wide region in such a manner that the devices are enlargedly spaced from each other in the wide region, thereby obtaining a relatively large display unit such as an image display unit. For example, U.S. Pat. No. 5,438,241 has disclosed a thin film transfer method, and Japanese Patent Laid-open No. Hei 11-142878 has disclosed a method of forming a transistor array panel for display. In the transfer method disclosed in U.S. Pat. No. 5,438,241, devices densely formed on a substrate are coarsely re-arrayed by transferring the devices densely formed on the substrate to an extensible substrate provided with an adhesive layer, extending the extensible substrate in the X direction and the Y direction while monitoring a device array pitch and positions of respective devices, and transferring the devices on the extended substrate onto a desired display panel. In the technique disclosed in Japanese Patent Laid-open No. Hei 11-142878, thin film transistors forming a liquid crystal display portion on a first substrate are all transferred onto a second substrate, and the thin film transistors are selectively transferred from the second substrate to a third substrate in such a manner that the transferred transistors are spaced from each other on the third substrate with a pitch corresponding to a pixel pitch.
In the case of thin display units such as LCDs and PDPs, as is apparent from characteristics of the production process thereof, a defective (non-activated) pixel inevitably occurs, and such a defective pixel cannot be repaired. Meanwhile, in the case of display units using LEDs as emission sources, since all of the pixels are mounted independently from each other, if a non-activated pixel is detected in an emission test performed after completion of all of the production steps, then such a defective pixel can be repaired, in principle. However, if the defective device is repaired in the usual manner, then the repair requires complicated, microscopic works such as removal of the defective device forcibly fixed, and repair of an insulating layer, and the like.